A new problem has just been presented to the profession of obstetrics. Testart and coworkers report that exposure of the human ovary to diagnostic ultrasound may result in premature ovulation. Whether this is a true effect of ultrasound must be studied critically. Certainly, these experiments must eventually be replicated in other clinics. However, the Testart report, in itself, places certain ethical limitations upon continued experoimentation with human subjects. It is essential that the effects of diagnostically relevant, pulsed ultrasound on ovulation be studied in laboratory animals as soon as possible. It is required not only because of these ethical considerations but because in laboratory experiments the subject can be explored in greater detail and under extreme exposure conditions that would not be permitted under any circumstances with human subjects. The objective if the proposed research is to determine whether pulsed ultrasound exposure after ovulatory gonadotropin stimulate causes premature ovulation using a laboratory mouse under experimental conditions which mimic the Testart human studies. The physical conditions of exposure will be chosen to maximize the probability of acoustic cavitation while controlling the producation of heat.